The present invention relates to machine tools in general, and more particularly to improvements in milling, grinding, boring and similar material removing machines. Still more particularly, the invention relates to improvements in machine tools for removal of material from workpieces which are mounted on a work supporting table or the like in or on the frame or base of the machine, and wherein an upright or otherwise oriented carrier supports a vertical or otherwise inclined work spindle which can receive tools from a magazine on the machine frame.
It is well known to provide a machine tool (also called a machining center) with a magazine for a supply of spare tools and with means for transferring tools between the spindle and the magazine. The presently known and utilized tool magazines normally belong to one of the following four categories:
(1) In accordance with a first prior proposal, the tool magazine is fixedly mounted in or on the frame of the machine at a location which is remote from the tool spindle when the tool on the spindle is ready to treat a workpiece. The spindle is movable in directions toward and away from the magazine so that it can assume a plurality of different positions with respect to the contents of the magazine. In each such position, the spindle can receive from the magazine a different tool or can deliver a tool to a different portion of the magazine. The just described tool storing and transferring system is relatively simple and inexpensive. However, it also exhibits a number of serious drawbacks, especially that replacement of a first tool on the tool spindle with a different second tool takes up a relatively long interval of time. Furthermore, the duration of each interval of tool transfer is different because it depends upon the distance between the normal or operative position of the tool spindle and the location of a selected tool in the interior of the stationary magazine. This is due to the fact that each and every tool is allotted a predetermined position in the interior of the magazine and that the latter does not have any means for transferring tools in its interior to a position at a minimum distance from the tool spindle when the spindle is held in the operative position. Nevertheless, such magazines continue to be in use because they can be installed at a considerable distance from the operative position of the tool spindle so that the interior of the magazine and the tools therein cannot be contaminated by chips, shavings and/or other particles which are removed from the workpiece when the tool on the spindle is in actual use.
(2) In accordance with a second prior proposal, the tool magazine is indexible so that it can place a selected tool to a predetermined position in which such tool can be transferred onto the tool spindle and the magazine can receive the previously utilized tool from the spindle. As a rule, the transfer of tools takes place in such a way that the spindle is advanced toward the magazine, the tool is transferred from the spindle into the magazine, and the magazine is thereupon indexed to move a selected tool into proper position for transfer onto the spindle. This entails relatively long periods of dwell of the spindle at a considerable distance from the operative position with attendant long interruptions of treatment of workpieces. The periods of dwell vary from transfer to transfer because their duration depends upon the extent to which the magazine must be indexed after it has received a previously used tool from the spindle.
(3) In accordance with a third conventional proposal, the magazine which stores a supply of spare tools is indexible in a machine tool wherein the work spindle is movable in a single direction, namely in the direction of the Z-axis which makes an angle of 90 degrees with the general plane of the magazine and is normally vertical. The magazine can index a selected tool into the path of movement of the spindle in the direction of the Z-axis. When a selected tool is located in the path of movement of the spindle, the latter is advanced from a retracted position to a coupling position, in which it is connected with the selected tool, and thereupon to an operative position in which it can treat a workpiece. This means that the interval which is required for the attachment of a fresh tool to the spindle is reduced considerably because the spindle can proceed from the tool-receiving position to the operative position without any delay as soon as a selected tool is properly positioned with reference to the path of movement of the spindle along the Z-axis. The transfer of a previously used tool back into the magazine takes place by reversing the direction of movement of the spindle so that the latter is moved from the operative position to the tool transferring position in which the previously used tool is detached therefrom, and the spindle is thereupon advanced to the retracted position so as to allow for renewed indexing of the magazine in order to place a different tool into the path of movement of the spindle toward its operative position.
The just described system exhibits a serious drawback, namely that the magazine is closely adjacent to the station where the tool on the spindle treats the workpieces. This brings about the danger of contaminating the tools in the interior of the magazine by chips, shavings and/or other particles which are being removed from a workpiece. Furthermore, if the tool which has been coupled to the spindle was located between a pair of relatively large spare tools in the interior of the magazine, such spare tools are likely to interfere with movements of a workpiece to a desired number of different positions for proper treatment by the tool which is then mounted on and is rotated or otherwise moved by the spindle. An additional drawback of the just described system is that the efficiency of tool transfer between the spindle and the magazine depends considerably on the distribution of spare tools in the interior of the magazine and on the sequence in which the tools are to be connected with the spindle. In other words, the transfer can be effected rapidly and efficiently only if the tool which is about to be attached to the spindle is not remote from the position to which such tool must be indexed with the magazine in order to be located in the path of movement of the tool spindle from its retracted to its operative position.
(4) In accordance with a fourth proposal, the tool magazine is indexible about a fixed axis and is installed in the machine frame at a location which is remote from the operative position of the tool spindle. The magazine can be indexed by a suitable stepping motor or the like so as to move a selected tool to a predetermined position with reference to the tool spindle. Such machine further comprises a so-called manipulator with two pairs of grippers or jaws. The manipulator is installed in the space between the tool spindle and the locus of the selected position of a tool which is about to be transferred onto the spindle. One pair of jaws which form part of the manipulator can receive and hold a tool which has been removed from the spindle, and another pair of jaws on the same manipulator can grip the tool which is about to be attached to the spindle. Once the manipulator supports two discrete tools, it is indexed (normally through an angle of 180.degree.) so as to place the tool which has been removed from the magazine into proper position for application to the tool spindle and to place the tool which has been removed from the spindle into proper position for insertion or introduction into the magazine.
The just described system exhibits the important advantage that the interval which is required for the transfer of tools between the magazine and the tool spindle is reduced considerably because the indexing of the magazine in order to place the tool, which is about to be transferred onto the spindle, into an optimum position for such transfer can take place while a tool is still attached to the spindle and is in actual use. An additional advantage of such system is that the magazine and the tools therein are remote from the location where the tool on the spindle treats the workpieces so that the tools which are stored in the magazine are not likely to be contaminated by cutting liquid, grease and/or particles of material which is being removed from the workpieces. In addition, the tools which are stored in the magazine cannot interfere with movements of the workpiece to any desired number of different positions relative to the tool which is then attached to the spindle. However, such system also exhibits a serious drawback, especially as concerns its complexity and initial and maintenance cost. This will be readily appreciated by bearing in mind that the manipulator must be equipped with at least three electromechanical, hydraulic, pneumatic or other drives in order to enable the manipulator and its jaws to perform a requisite number of different movements, namely the jaws must be capable of performing a movement between open and closed positions in which they respectively release and engage a tool, the manipulator must be capable of performing a second movement which enables a pair of jaws to attach a tool to or to remove a tool from the spindle, and the manipulator must be capable of performing a third movement (normally an indexing movement through 180.degree.) in order to move one pair of jaws from a position in close proximity to the spindle to a position close to the magazine while the other pair of jaws moves from a position close to the magazine to a position closer to the spindle.